1. Field of the Invention
This invention relates to a method and apparatus for carrying out image processing on a binary image signal, which is obtained from a computer, an image read-out apparatus, or the like. This invention particularly relates to a character pattern and line pattern thickening processing (hereinbelow referred to simply as the thickening processing) for thickening a character pattern and a line pattern in a binary image, which is represented by a digital signal.
2. Description of the Prior Art
In cases where binary images, which have been formed with application software functions, such as word processors in computers, or binary images, which have been read out with image read-out apparatuses, such as image scanners, are printed by using digital stencil printers, the problems are often encountered in that small character patterns or thin character patterns become blurred on the obtained prints. Also, several fonts used in application software functions in computers have the problems in that, when the character patterns and line patterns belonging to the fonts are printed by using digital stencil printers, printed images, which look thin and weak, are obtained. Further, besides digital stencil printers, with devices for printing binary images, including character patterns and line patterns, which are represented by digital signals, such as printers for personal computers and facsimile devices, the problems are often encountered in that the printed small character patterns and thin character patterns become blurred and cannot easily be perceived visually.
In order to prevent the printed images from becoming blurred or looking thin and weak (hereinbelow referred to as the blurring, or the like), an image forming apparatus, which expands a character pattern or a line pattern in a binary image by simply adding black picture elements to the upper position, the lateral position, and the oblique position with respect to a black picture element in the binary image. Such an image forming apparatus is proposed in, for example, Japanese Unexamined Patent Publication No. 6(1994)-152932.
As another technique for preventing a printed image from blurring, or the like, a technique has been proposed, wherein a contour of a binary image is discriminated and the thickness of a line is changed in accordance with the results of the discrimination such that the contour may be retained. Such a technique is proposed in, for example, Japanese Unexamined Patent Publication No. 3(1991)-16758.
However, the conventional techniques described above has the practical problems described below.
Specifically, the technique proposed in Japanese Unexamined Patent Publication No. 6(1994)-152932 has the problems in that a blank region, which is to be kept as a blank, becomes black and is lost. The problems will be described hereinbelow with reference to FIGS. 18 and 19, which show an example of the thickening processing carried out on a binary image signal by the utilization of the proposed technique. FIG. 18 is a matrix diagram showing an example of an original binary image to be subjected to thickening processing. FIG. 19 is a matrix diagram showing a binary image, which is obtained from thickening processing carried out on the original image of FIG. 18 by using an example of conventional technique (proposed in Japanese Unexamined Patent Publication No. 6(1994)-152932). With the proposed technique, black picture elements are simply added to the upper position, the left position, and the upper left position with respect to a black picture element in the original image. Therefore, in cases where the thickening processing is carried out with the proposed technique, a white picture element, which is surrounded by a plurality of black picture elements, and a white picture element, which is sandwiched between adjacent black picture elements, are converted into black picture elements. Accordingly, it often occurs that a region, which is to be recorded as a blank, becomes black and is lost. For example, the two lower blank regions among the four blank regions, which are defined by the three vertical black lines and the three horizontal black lines at the upper half of the right-hand radical of the Chinese character pattern in the original image shown in FIG. 18, become black and are lost as illustrated in FIG. 19. Also, the blank region, which is located between the left-hand radical and the right-hand radical of the Chinese character pattern, becomes black and is lost as illustrated in FIG. 19. As a result, the problems occur in that the image becomes unsharp and hard to see and cannot be read. Also, the character pattern, in which the blank regions that are to be retained have become black and have been lost, cannot give a good aesthetic feeling to persons who see it.
With the technique proposed in Japanese Unexamined Patent Publication No. 3(1991)-16758, the thickness of a line can be changed such that a blank region may not become black and may not be lost. However, the proposed technique has the drawbacks in that very complicated discrimination processing must be carried out in order to discriminate the contours of character patterns and line patterns in a binary image.